Individual Lifetime Reproductive Success Research Articles

Do females of Whiskered Tern Chlidonias hybrida renest after offspring desertion?

In species with biparental care, one parent may relieve him-/herself of the costs of parental care by deserting and leaving the mate to care for the offspring. Offspring desertion by a single parent, usually the female, occurs in many bird species, especially in Charadriiformes. The reasons for desertion are still being debated, and compelling evidence for the benefits and costs to either sex is not yet handed. The benefits of desertion for the deserter may include renesting with a new mate shortly after desertion. Therefore, desertion may enhance individual lifetime reproductive success. In Whiskered Tern Chlidonias hybrida almost all females desert, about half of females desert during chick-rearing period, the other half during the post-fledging period. Based on intensive fieldwork over a 4-year study, we investigated whether Whiskered Tern females remated and renested after desertion. We assumed that favourable conditions, such as an extended breeding season and food abundance resulting in a high breeding success would prompt most females to renest after desertion. In contrast to this expectation, however, only 5% of females that deserted during chick-rearing period (2 out of 41) remated and renested in the study area. About 50 days elapsed between the initiations of the first and second clutch by these two females. Females also participated in courtship behaviour after desertion (without renesting). We thus estimate that 15% (6 out of 41) of females that deserted during chick-rearing period were subsequently involved in some kind of breeding activity. Therefore, renesting does not seem to be a major direct benefit for deserting Whiskered Tern females. Females of this species probably benefit from desertion in other ways, but these have yet to be discovered.

Captive-bred Atlantic salmon released into the wild have fewer offspring than wild-bred fish and decrease population productivity.

The release of captive-bred animals into the wild is commonly practised to restore or supplement wild populations but comes with a suite of ecological and genetic consequences. Vast numbers of hatchery-reared fish are released annually, ostensibly to restore/enhance wild populations or provide greater angling returns. While previous studies have shown that captive-bred fish perform poorly in the wild relative to wild-bred conspecifics, few have measured individual lifetime reproductive success (LRS) and how this affects population productivity. Here, we analyse data on Atlantic salmon from an intensely studied catchment into which varying numbers of captive-bred fish have escaped/been released and potentially bred over several decades. Using a molecular pedigree, we demonstrate that, on average, the LRS of captive-bred individuals was only 36% that of wild-bred individuals. A significant LRS difference remained after excluding individuals that left no surviving offspring, some of which might have simply failed to spawn, consistent with transgenerational effects on offspring survival. The annual productivity of the mixed population (wild-bred plus captive-bred) was lower in years where captive-bred fish comprised a greater fraction of potential spawners. These results bolster previous empirical and theoretical findings that intentional stocking, or non-intentional escapees, threaten, rather than enhance, recipient natural populations.

Lifetime reproductive success of northern elephant seals (Mirounga angustirostris)

Lifetime reproductive success of individuals in a natural population provides an estimate of Darwinian fitness. We calculated lifetime reproductive success in a colony of female northern elephant seals (Mirounga angustirostris (Gill, 1866)) by monitoring annual breeding throughout life of 7735 female weanlings marked individually at Año Nuevo, California, USA, from 1963 to 2005. Great variation in lifetime reproductive success was evident in three aspects of life history: (1) 75% of the females died before reaching breeding age and produced no pups; (2) nearly half of the survivors bred for only a few years before dying, and young females had low weaning success; (3) less than 1% of the females in the sample were exceptionally successful producing up to 20 pups in life. Many females that bred early, while still growing, had decreased lifespan, low weaning success, and lower lifetime reproductive success than females that postponed first breeding. Exceptional reproductive success was associated with giving birth annually, living long (up to age 23), and weaning large pups that were more likely to survive and breed. We conclude that there is strong selection for increased lifespan and multiparous supermoms that contribute significantly to pup production in the next generation.

Sweepstakes reproductive success is absent in a New Zealand snapper (Chrysophrus auratus) population protected from fishing despite "tiny" Ne /N ratios elsewhere.

A landmark study published in 2002 estimated a very small Ne /N ratio (around 10-5 ) in a population of pink snapper (Chrysophrys auratus, Forster, 1801) in the Hauraki Gulf in New Zealand. It epitomized the tiny Ne /N ratios (<10-3 ) reported in marine species due to the hypothesized operation of sweepstakes reproductive success (SRS). Here we re-evaluate the occurrence of SRS in marine species and the potential effect of fishing on the Ne /N ratio by studying the same species in the same region, but in a population that has been protected from fishing since 1975. We combine empirical, simulation and model-based approaches to estimate Ne (and Nb ) from genotypes of 1,044 adult fish and estimate N using recapture-probabilities. The estimated Ne /N ratio was much larger (0.33, SE: 0.14) than expected. The magnitude of estimates of population-wide variance in individual lifetime reproductive success (10-18) suggested that the sweepstakes effect was negligible in the study population. After evaluating factors that could explain the contrast between studies - experimental design, life history differences, environmental effects and the influence of exploitation on the Ne /N ratio - we conclude that the low Ne of the Hauraki Gulf population is associated with demographic instability in the harvested compared to the protected population despite circumstantial evidence that the 2002 study may have underestimated Ne . This study has broad implications for the prevailing view that reproductive success in the sea is largely driven by chance, and for genetic monitoring of populations using the Ne /N ratio and Nb .

Selection for life-history traits to maximize population growth in an invasive marine species.

Species establishing outside their natural range, negatively impacting local ecosystems, are of increasing global concern. They often display life-history features characteristic for r-selected populations with fast growth and high reproduction rates to achieve positive population growth rates (r) in invaded habitats. Here, we demonstrate substantially earlier maturation at a 2 orders of magnitude lower body mass at first reproduction in invasive compared to native populations of the comb jelly Mnemiopsis leidyi. Empirical results are corroborated by a theoretical model for competing life-history traits that predicts maturation at the smallest possible size to optimize r, while individual lifetime reproductive success (R0 ), optimized in native populations, is near constant over a large range of intermediate maturation sizes. We suggest that high variability in reproductive tactics in native populations is an underappreciated determinant of invasiveness, acting as substrate upon which selection can act during the invasion process.

An Overview of the Factors Influencing the Morphology and Thermal Properties of Avian Nests

Incubation in birds is energetically demanding and the energy invested to maintain egg temperature can influence the outcome of a reproductive event and therefore the lifetime reproductive success of individuals. It is reasonable that heat loss can be minimised by optimising the physical structure and location of the nest. I assessed the structural and thermal properties of nests across 36 species of Australian passerines, assessing variables against parent mass, egg and clutch size, once accounting for phylogenetic relationships. The surface area and volume of the nest cup increases with the surface area and volume of the clutch, as well as the size of the incubating parent. Sexual size dimorphism influences the mass and density of nests, while structural support for the parent and clutch is the primary factor driving nest thickness. A change in nest thickness with the combined mass of the parent and clutch has a direct influence on the conductance of nests, such that structurally adequate nests achieve a lower thermal conductance (higher insulation) than expected, as they increase in size. When exposed to wind or rain, the rate of heat loss from the nest increases, which is likely to have direct consequences on the energetics of the incubating parent. However, birds breeding in warm and wet conditions select materials for nest construction that have a high thermal conductivity to facilitate the nest drying process through rapid evaporation and reduce the overall cost of incubation. This provides confirmation that selecting a sheltered nest site and constructing an appropriate nest to minimise heat loss is important for avian reproductive success.

Timing of Puberty and Its Relationship with Body Growth and Season in Male Raccoons (&lt;i&gt;Procyon lotor&lt;/i&gt;) in Hokkaido

The raccoon (Procyon lotor), indigenous to North America, has naturalized in Japan as an invasive alien species, having been introduced into the country in the 1970s. In Hokkaido, the northernmost island of Japan, feral raccoons have been increasing in number and spreading throughout the island. The age at the onset of puberty for raccoons is important for estimating individual lifetime reproductive success and population growth. The present study investigated the timing of and potential factors affecting the onset of puberty in male raccoons in Hokkaido. External characteristics and histology of testes were studied in 151 male feral raccoons and in 1 captive juvenile. For the majority of feral yearling raccoons, prepubertal development began in May, and spermatozoa production began in October prior to their second mating season. However, some larger juveniles attained puberty during the juvenile period. The captive juvenile, which was fed throughout the winter, attained puberty only 11 months after birth. These results suggest that if male raccoons can achieve enough body growth before the first mating season, puberty can be attained early. In both juveniles and yearlings, spermatozoa production was only observed after autumn. This timing coincided with the recrudescence of seasonally active spermatogenesis in adult males. Therefore, attaining puberty in male raccoons appears to require both adequate body nutrient development and several environmental factors that control seasonal testicular changes.

Antagonistic Parent-Offspring Co-Adaptation

BackgroundIn species across taxa, offspring have means to influence parental investment (PI). PI thus evolves as an interacting phenotype and indirect genetic effects may strongly affect the co-evolutionary dynamics of offspring and parental behaviors. Evolutionary theory focused on explaining how exaggerated offspring solicitation can be understood as resolution of parent-offspring conflict, but the evolutionary origin and diversification of different forms of family interactions remains unclear.Methodology/Principal FindingsIn contrast to previous theory that largely uses a static approach to predict how “offspring individuals” and “parental individuals” should interact given conflict over PI, we present a dynamic theoretical framework of antagonistic selection on the PI individuals obtain/take as offspring and the PI they provide as parents to maximize individual lifetime reproductive success; we analyze a deterministic and a stochastic version of this dynamic framework. We show that a zone for equivalent co-adaptation outcomes exists in which stable levels of PI can evolve and be maintained despite fast strategy transitions and ongoing co-evolutionary dynamics. Under antagonistic co-adaptation, cost-free solicitation can evolve as an adaptation to emerging preferences in parents.Conclusions/SignificanceWe show that antagonistic selection across the offspring and parental life-stage of individuals favors co-adapted offspring and parental behavior within a zone of equivalent outcomes. This antagonistic parent-offspring co-adaptation does not require solicitation to be costly, allows for rapid divergence and evolutionary novelty and potentially explains the origin and diversification of the observed provisioning forms in family life.

Sex-specific patterns of lifetime reproductive success in single and repeat breeding steelhead trout (Oncorhynchus mykiss)

All other things being equal, the lifetime reproductive success (LRS) of iteroparous and semelparous individuals should scale with the number of breeding seasons. Deviations from this relationship may occur for many reasons, including age- or size-related fecundity or life history trade-offs, which may differ between sexes. We used 19 brood years of DNA parentage analysis in a small (N = 4–143 year−1) wild, unexploited population of steelhead trout (Oncorhynchus mykiss) to compare the LRS of individuals that spawned only once [“one time spawners” (OTS), N = 355 male, 371 female] to those spawning twice [“repeat spawners” (RPS), N = 13 male, 49 female]. Female RPS had nearly twice the LRS of female OTS (1.17 offspring per female vs 0.91 offspring per female), whereas male RPS had nearly three times the LRS of male OTS (1.54 offspring per male vs 0.57 offspring per male). Female RPS produced slightly more adult offspring during their second breeding season than their first (0.78 vs 0.82 offspring per female); however, male RPS produced all of their adult offspring in their second breeding season (0 vs 1.54 offspring per male). The additional growth in body size of males between breeding seasons may give them an advantage in their second breeding season, but the lack of offspring produced in their first season suggests a trade-off between survival and future reproduction that was not expressed in females.

A silver spoon for a golden future: long‐term effects of natal origin on fitness prospects of oystercatchers (Haematopus ostralegus)

1. Long-term effects of conditions during early development on fitness are important for life history evolution and population ecology. Using multistrata mark-recapture models on 20 years of data, we quantified the relation between rearing conditions and lifetime fitness in a long-lived shorebird, the oystercatcher (Haematopus ostralegus). We addressed specifically the relative contribution of short- and long-term effects of rearing conditions to overall fitness consequences. 2. Rearing conditions were defined by differences in natal habitat quality, in which there is a clear dichotomy in our study population. In the first year of life, fledglings from high-quality natal origin had a 1.3 times higher juvenile survival. Later in life (age 3-11), individuals of high-quality natal origin had a 1.6 times higher adult prebreeder survival. The most striking effect of natal habitat quality was that birds that were reared on high-quality territories had a higher probability of settling in high-quality habitat (44% vs. 6%). Lifetime reproductive success of individuals born in high-quality habitat was 2.2 times higher than that of individuals born in low-quality habitat. This difference increased further when fitness was calculated over several generations, due to a correlation between the quality of rearing conditions of parents and their offspring. 3. Long-term effects of early conditions contributed more to overall fitness differences as short-term consequences, contrary to common conceptions on this issue. 4. This study illustrates that investigating only short-term effects of early conditions can lead to the large underestimation of fitness consequences. We discuss how long-term consequences of early conditions may affect settlement decisions and source-sink population interactions.

Patterns and fitness consequences of intraclutch variation in egg provisioning in tropical Australian frogs

Intraclutch variation in offspring size should evolve when offspring encounter unpredictable environmental conditions. This form of bet-hedging should maximise the lifetime reproductive success of individuals that engage it. We documented the numbers of eggs and means and variances of yolk volume in 15 frog species that occur in tropical savanna woodland. We experimentally determined the effects of initial yolk volume on larval growth patterns in four species. Intraclutch variation in yolk volume occurred to some degree in all species surveyed. Some species had very low, others had very high, intraclutch variation in yolk volume, but all species in which some clutches were highly variable also produced clutches with low variability. Species that occur in areas where the offspring environment is likely to be unpredictable had elevated levels of intraclutch variation in egg provisioning. There was no trade-off between egg size and number in any species surveyed. Under benign laboratory conditions, tadpoles from eggs with larger yolk volumes hatched at larger sizes, and these size differences persisted through a substantial proportion of the larval stage. This indicates that intraclutch variation in egg size has major offspring and thus parental fitness consequences, and is therefore a functional selection variable. This study provides evidence in support of models which predict that intraclutch variation in offspring provisioning can evolve in organisms that reproduce in unpredictable habitats.

Brood desertion and polygamous breeding in the Kentish Plover Charadrius alexandrinus

In the Kentish Plover Charadrius alexandrinus one of the adults, typically the female, deserts the brood when the chicks are a few days old. Once parental care is terminated, adults may initiate a second nesting attempt if sufficient time remains within the season. For these nests, individuals pair with different mates from those of the first nesting attempt, thus becoming sequentially polygamous. In a small population of Kentish Plovers in Fuente de Piedra lake (southern Spain), the duration of biparental care of broods was longer than in other localities. It also showed considerable variation between years that was evidently related to Gull‐billed Tern Gelochelidon nilotica predation pressure on the chicks. There was year‐to‐year variation in the number of polygamous matings. Both the duration of the breeding season and nesting success in the first half of the season limited the occurrence of polygamy. Despite females deserting broods earlier than males, the interval between the first and second nesting of polyandrous females and polygynous males was similar. The interval was not affected by the body condition of females after the first nesting attempt, nor by problems related to egg formation ability, but was probably due to the availability of potential mates. More females than males initiated second nests, suggesting that polygamous opportunities were more limited for males than for females. In terms of delayed breeding, reduced survivorship or reduced breeding opportunities in years following polygamous breeding, polygamous individuals did not have greater costs than non‐polygamous ones. Females with second nests did not seem to be selective in mate choice, mating with any available male. Mates for second nests may therefore be of lower quality than those for first nests, as judged by male plumage characteristics. Clutch sizes and egg characteristics of polyandrous females were similar in first and second nests. Nest success of second nests was only 40% of that of first ones, with nest desertion accounting for 60% of the losses. As the costs of polygamy are apparently low and as breeding success is very variable among years, polygamous breeding of the long‐lived Kentish Plover may be an important breeding strategy with which to increase individual lifetime reproductive success.

Constraints on First Reproduction in North American Red Squirrels

Age at first reproduction influences lifetime reproductive success of individuals and growth rates of populations, and is thus of general interest to ecologists. In red squirrel (Tamiasciurus hudsonicus) populations, yearlings and older nulliparous females (age two and above) are less likely to have a litter than multiparous females (i.e. those that have bred before). To explain these life history traits we tested several hypotheses for why particular females fail to breed in a given year. In a five-year study of red squirrels in a jack pine (Pinus banksiana) forest in central Alberta, Canada, the probability of primiparity (i.e. producing a litter for the first time) was correlated with cone crop size, but doubling the caches of cones available to females failed to increase the probability of first time reproduction. Cones were never completely depleted on any territory, so first reproduction rarely appeared to be restricted by absolute food availability on a territory. We hypothesize, that first reproduction is constrained by the squirrel's ability to obtain seed energy enclosed in serotinous cones that vary in distribution on a territory. We found that the probability of primiparity is lower and more variable between years than that of multiparity, because foraging and cone-handling efficiencies vary more in younger than in older squirrels. Nulliparous females given sunflower seeds to reduce handling time were two to six times more likely to produce a first litter than controls extracting seed from jack pine cones. Small body size, inexperience with seed extraction from serotinous cones, and a lack of strategies for gathering and using cones from a new territory are supported as mechanisms that constrain primiparity, especially in yearlings. Cold spring temperatures added a further constraint in one year, as did absolute cone crop size. Multiparous females strip the bracts off cones in the autumn, reducing handling costs in winter and spring, while young nulliparous females lacked such behavioural compensation. In jack pine, reproductive success of red squirrels depends upon behaviour adapted to a seed supply that is abundant but costly to extract from serotinous cones.

Validity of an estimator of reproductive success.

Lifetime reproductive success is a major component of individual fitness and a central dependent variable for the study of natural selection. For long-lived animals, such as apes or baboons, assessment of lifetime reproductive success requires observations of identified individuals in continuous, long-term studies from which it is difficult and often impossible to obtain an adequate sample of necessary reproductive and survival data. This situation can be alleviated by the availability of a valid measure that uses incomplete reproductive histories to estimate the lifetime reproductive success of individuals. The validity of one such estimator was tested by determining if, after 10.5 years of studying free-ranging female baboons, it predicted lifetime reproductive success obtained from full reproductive histories after 21.5 years. Validity was evaluated for seven criteria of success, ranging from the number of a female's live births to the number of her offspring that reached the age of 72 months. Moderate to good prediction of lifetime reproductive success by the estimator was found for criteria of offspring living to 36 months or more. After 10.5 years, complete reproductive life spans were available for only eight females. Using the estimator, analytic potential, via sample representativeness and size, was improved at 10.5 years by an increase from a sample of eight to between 34 and 62, depending upon the criterion used, and at 21.5 years from 39 to 70. With a valid estimator, the opportunity to study lifetime reproductive success of a long-lived species is substantially improved without having to depend upon rarely available, uninterrupted data collection for 20-60 years.

Validity of an estimator of reproductive success

Lifetime reproductive success is a major component of individual fitness and a central dependent variable for the study of natural selection. For long-lived animals, such as apes or baboons, assessment of lifetime reproductive success requires observations of identified individuals in continuous, long-term studies from which it is difficult and often impossible to obtain an adequate sample of necessary reproductive and survival data. This situation can be alleviated by the availability of a valid measure that uses incomplete reproductive histories to estimate the lifetime reproductive success of individuals. The validity of one such estimator was tested by determining if, after 10.5 years of studying free-ranging female baboons, it predicted lifetime reproductive success obtained from full reproductive histories after 21.5 years. Validity was evaluated for seven criteria of success, ranging from the number of a female's live births to the number of her offspring that reached the age of 72 months. Moderate to good prediction of lifetime reproductive success by the estimator was found for criteria of offspring living to 36 months or more. After 10.5 years, complete reproductive life spans were available for only eight females. Using the estimator, analytic potential, via sample representativeness and size, was improved at 10.5 years by an increase from a sample of eight to between 34 and 62, depending upon the criterion used, and at 21.5 years from 39 to 70. With a valid estimator, the opportunity to study lifetime reproductive success of a long-lived species is substantially improved without having to depend upon rarely available, uninterrupted data collection for 20–60 years. Am. J. Primatol. 44:137–145, 1998. © 1998 Wiley-Liss, Inc.

Intercolonial encounters and xenophobia in the common mole rat, Cryptomys hottentotus hottentotus (Bathyergidae): the effects of aridity, sex, and reproductive status

The ecological constraints prevalent in arid environments have promoted the evolution of social groups with a high reproductive skew in mole rat species occurring there. Outbred social bathyergids face conflict between maintaining colony integrity to enhance personal foraging success and hence survival, and dispersal to maTimizr individual lifetime reproductive success (LRS). This conflict will be a crucial determinant of the response of colony members to the presence of foreign conspecifics. We investigated how ecological constraints, sex, and reproductive status influence die outcome of meetings between foreign common mole rats (Cryptomys hottentotus hottentotus) in a series of dyadic encounters. Individuals from two localities, at the extremes of an aridity gradient, were used to assess the effects of aridity. The efFects of sex and reproductive status were investigated by trials between individuals of differing sex and status. The arid population revealed substantially higher levels of rejection than the mesic population. Sex and status played a significant role in moderating individual response. For both populations, encounters between different-sexed individuals produced lower levels of rejection than those between same-sexed individuals. For the mesic site, rejection was greatest for encounters between reproductive animals. Conversely, for the arid site, the levels of rejection were comparatively high and comparable for all combinations of reproductive status. Ecological constraints, sex, and reproductive status are significant factors in interactions between foreign common mole rats, ultimately influencing individual survival, colony integrity and the differential LRS of all colony members. Our results provide insight into die evolution and maintenance of family groups within the bathyergids.

Reproductive Conflicts and Levels of Selection in the Ant Pristomyrmex pungens: Contextual Analysis and Partitioning of Covariance

Phenotypic selection on individual- and colony-level characters was examined in the myrmicine ant Pristomyrmex pungens by contextual analysis and partitioning of covariance. Pristomyrmex pungens has an extraordinary social system in which there are no queens and workers reproduce parthenogenetically. All workers can be reproductive and live only one year in this species. Thus, the annual colony growth rate measures the mean individual lifetime reproductive success. Within-colony individual variation in reproductive activity was estimated from individual ovarian development and revealed conflicting selection on worker dimorphism. Large workers are sporadically found in some colonies and had higher fitness on a within-colony level. However, large workers reduced a colony's fitness at the between-colony level. Therefore, large workers probably exist as a socially parasitic phenotype. Stabilizing and positive directional selection on the proportion of foragers appeared to be responsible for the evolutionary maintenance of cooperative breeding in this species. Cheaters that reproduce but never forage will be eliminated by colony-level selection. Overall, directional selection favored smaller colony size. Colony-level adaptation is important, because the mode of colony foundation, fission, is likely to enhance additive genetic variance of colonies and create the opportunity for a genetic response to colony-level selection.

Male quality, reproduction, and survival in the great tit (Parus major)

Three possible measures of male quality (social dominance, song, and size), reproduction, and survival were studied in a single population of great tits. Winter dominance position on a feeder was related to strophe length (number of phrases per strophe), inversely related to positive drift (decrease of the singing rate of the phrases in a strophe), but not related to song repertoire size. Neither winter dominance position nor song were related to size (wing length, tarso-metatarsus length, weight). Singing capacity was not correlated with individual reproductive success in a single breeding season, using a rather limited data set. However, “better” singers (males which sing longer strophes, show less positive drift, and have larger song repertoires) survived better and had a higher individual lifetime reproductive success (on the basis of a male's recruited offspring of all breeding seasons). Our results show that there exist measurable differences whereby birds that are dominant in winter sing “better”, survive longer, and produce more surviving offspring during their life time. We suggest that differences in male quality are the common cause (direct and indirect) of all these effects.